This invention relates to apparatus for imparting to a shaft either rotation or translation or both.
The capability for imparting to a shaft both rotary and linear motion has many desirable advantages. The advancing and rotating chuck of a drill press is a common embodiment of one such advantage. The patents of Moore (U.S. Pat. No. 885,945) and Doubet (U.S. Pat. No. 1,013,281) illustrate early application in this art.
A different use of this advantage is found in Gill (U.S. Pat. No. 1,413,982) wherein an embodiment is used to detect differences in the rotational speeds of two systems. Later embodiments in the art have developed for the robotic movement of a shaft or of a member attached to a shaft, such as Fornataro (U.S. Pat. No. 3,483,765) and Martin et al (U.S. Pat. No. 3,805,629).
A common feature of all these prior art devices provides for translation of a threaded shaft of circular cross section by rotating a threaded gear around the shaft while restraining the rotation of the shaft; coupled with this is another member which can rotate the shaft. In all of these devices there is used a threaded shaft which has threads substantially circumferential to and running the length of travel of the shaft. The threads are typically interrupted only by the use of one or two keyways running the length of travel of the shaft.
By the present invention there is provided an improved apparatus for imparting to a shaft either rotation or translation or both, by the rotation of one or both of two gears within the apparatus. Translation is provided by the rotation of a first gear having internal threads, which threads match a toothed rack superimposed upon a shaft which passes through the gear. Rotation of the shaft is provided by the rotation of a second gear which is slotted to match the shaft and rack which passes through the second gear. The separate elements of first gear, second gear, and racked shaft are each held in position relative to the other elements so as to allow desired movement of the elements while restraining all other movements.
Since the threaded rack is superimposed on the shaft, an existing unthreaded shaft may be employed on which a rack may be added. A further advantage and object of the invention is the ability with this apparatus to use a shaft of any geometric cross-section. An additional advantage and object of the invention is the use of a shaft having a minimum of threaded surface.
The gears of the present apparatus may be rotated by any suitable means and different means may be employed for the different gears. Other objects and advantages of the invention are described in the specification, drawings and claims.